Why Temptation?
Fiendish Codex II: Tyrants of the Nine Hells is one of my favorite supplements put out by Wizards of the Coast. I love the concept of soul harvesting, the rules for Faustian pacts, and the descriptions of devil society. It’s a fantastic book, and it certainly made me think about how I might run a devil-themed adventure.
On the other hand, I don’t think this book did an effective job of presenting ways to introduce such concepts into your campaign. Take, for example, the Faustian pact. It’s a novel idea, but no matter how tempting a particular devil’s offer might be, it’s hard to imagine the PCs ever signing such a contract. In fact, I think the moment the players hear the words ‘devil’ and ‘contract’ in the same sentence, they’re either going to head for the hills, or wind up stabbing sharp objects into the devil’s squishy bits. But let’s imagine for a moment that they do sign the contract. Where does that take the campaign? Are there in game consequences for engaging such behavior? One would certainly hope that signing a Faustian pact would take the campaign in a direction like this. However, when your players tend to roleplay like this, it’s hard to imagine such an outcome.
Besides, the Faustian pact is something that devils generally employ only when someone has already traveled well down the path of temptation. To get a character to take such a journey in the first place requires an incredible amount of subtlety and manipulation on the part of the DM, and when players can see through even the most intricately constructed lie with a successful Intuition check, it’s difficult to imagine sustaining such machinations for long.
That’s why I think a mechanic, like temptation, is so necessary. I feel like there needs to be a way to start players down the path to ruin without requiring a lot of effort on the DM’s part. I also feel like it shouldn’t matter if the players kill the villain, because it doesn’t address the larger issue of their own culpability. Finally, I feel like exposure to temptation should make a person more willing to trust evil creatures, much like how Frodo trusted Gollum, or how Bastian trusted Xayide. After all, if temptation is like a drug, then evil creatures are the pushers, and characters are much more likely to trust them if they feel like they’re the most likely source of their next fix.
Now some might ask why not just use a mechanic like taint? Well first, I would point out that taint doesn’t really represent temptation. Rather, it represents one’s physical or psychological reaction to witnessing horrific events. If you want to represent what happens when a character first lays eyes on the Great Old Ones, then taint is a great mechanic. If you want to represent what happens when a character first encounters the evil wizard, Hertzog, then you really need something else.
Third Edition House Rules 
It obviously depends on your groups, but mechanics-based slides into temptation do not seem that interesting to me. If you are not playing with a group that wants to grapple with questions of philosophy and what does it mean to be evil, why bother running a temptation subplot? That is not to say that they are not interesting rules but I fail to see how they are going to help create the roleplaying experience you want out of temptation unless the players are, well, tempted by playing out such a campaign in the first place.
I completely agree. If you’re not playing with a group that enjoys dealing with deep, moral, and ethical issues in game, temptation is a pretty useless mechanic. In fact, I could even see how it might frustrate players who are more interested in things like killing monsters and taking their stuff, because it gets in the way of… well… killing monsters and taking their stuff. On the other hand, if you are playing with a group that does enjoy these types of themes, then a mechanic like temptation can really help you tell your story.
In my opinion, a game mechanic, like temptation, is like a director’s note given to an actor. It helps players understand what’s happening in the story, and what they might be thinking or feeling at a particular moment. In the hands of a player who isn’t interested in roleplaying, a mechanic like temptation is like a director’s note given to a person who isn’t interested in acting. The only way a mechanic like this works is if you have players who are interested in roleplaying. Otherwise, I’ll admit, it’s a pretty useless mechanic.
You put a lot of work into them and they are solid mechanically. Which I appreciate. But we need to work with our players.